METHODS OF ANALYSIS. 39 
of concentrated arsenic-free nitric acid and 5 ce of concentrated arsenic-free 
sulphuric acid, allow the first violent action to subside, and then put on an 
iron plate and gradually heat to boiling. Continue boiling till the liquid begins 
to darken. When this occurs, add concentrated arsenic-free nitric acid in quan- 
tities of 3 cc at a time, until on further heating it continues colorless and fumes 
strongly of sulphuric acid. Cool, dilute with 10 ce of arsenic-free water, and 
boil to break up the nitro-sulphurie acid formed. When cool, dilute with water 
and deliver into the Marsh-Berzelius apparatus previously described. 
Soluble arsenic. 
Weigh from 1 to 3 grams of the finely ground cattle food, according to the 
amount of soluble arsenic present, and transfer to a beaker. Extract on the 
steam bath with 50 to 100 ce of water for four hours. Filter, wash, and eyapo- 
rate the filtrate to a small bulk. Transfer to a 200 ce Jena flask and evaporate 
to only a few cubic centimeters. Add 25 cc of concentrated arsenic-free nitric 
acid and 5 ce of concentrated arsenic-free sulphuric acid and proceed as in the 
preceding method for total arsenic. 
ORES. 
Sulphur. 
Treat 0.5 gram of the ore in a 6-oz. flask with 10 ce of strong nitric acid. 
Heat very gently until the red fumes have somewhat abated, and then add 
potassium chlorate in small portions at a time (about 0.2 to 0.8 gram) until 
any free sulphur that has separated is entirely oxidized and dissolved. The 
acid should not be boiled violently, nor should it simply simmer. When 
the sulphur has entirely disappeared, boil the solution to complete dryness. 
(This may be hastened by manipulating the flask over a free flame.) After 
cooling cautiously add 5 ce of strong hydrochloric acid. If iron oxid, ete., still 
remains undissolved, gently heat the hydrochloric acid mixture until solution 
is as complete as possible, adding more acid, if necessary. Finally boil to dry- 
ness. Repeat this operation. Take up once more in 5 ce of hydrochloric acid 
and dilute with about 100 ce of hot water. Make alkaline with ammonia and 
then add 10 ce of a saturated solution of ammonium carbonate in order to con- 
vert any lead sulphate present to carbonate and thus render the combined SOs; 
soluble aS ammonium sulphate. Heat to boiling, allow ferric hydroxid, ete., to 
settle, filter, and wash very thoroughly with hot water, receiving the filtrate 
in a large beaker. 
Neutralize with uydrochloriec acid and add 5 ce extra. Dilute to about 300 
ee and precipitate with barium chlorid in the ordinary way. 
Arsenic.& 
Thoroughly mix 0.5 gram of the finely ground ore in a large platinum crucible 
with 5 grams of a mixture of equal parts of dry sodium carbonate and potas- 
sium nitrate. Reserve a portion of the mixed salts for use as a cover. Heat 
the mass gradually over a Bunsen flame to complete fusion. Use a very low 
flame at first and take plenty of time to avoid loss of arsenic by volatilization. 
Finally heat to the full power of the Bunsen burner until thoroughly decom- 
posed. The melted mass should finally present a smooth and homogeneous 
appearance. Cool, extract the soluble portion by heating with water, and 
filter and wash the residue with hot water. Drop a piece of litmus paper into 
the filtrate and make slightly acid with nitric acid, adding enough to dis- 
2Low’s Technical Methods of Ore Analysis, 
